This invention relates to beams of igneous rock.
It has long been known that igneous rock materials are extremely stable. Granite, for example, has a very low coefficient of thermal expansion, and very high tensile strength. As such, granite and like igneous rock materials have been widely accepted in the building and industrial arts where a material of high stability is required.
In particular, beams of granite have been used to fabricate precision guide surfaces for various precision instruments, such as coordinate measuring machines and circuit board drilling machines. Granite heretofore, however, has not proved to be a completely satisfactory material for such uses, largely because of its weight. Granite is very dense, and therefore a solid granite beam of a given size significantly outweighs an analogous hollow beam of steel, aluminum, or cast ceramics. Manufacturers of precision instruments have increasingly been using these materials in lieu of granite on account of lower transport costs, stress tolerances, and other weight-related factors. These materials, however, have also proved to be unsatisfactory. Cast ceramics, for example, has similar tensile strength and thermal expansion properties as igneous rock, but are generally much more expensive. On the other hand, steel and aluminum have higher coefficients of thermal expansion.